Originally, computer networks were designed to have a centralized, network topology. In such a topology, a centralized mainframe computer is accessed by users at computer terminals via network connections. Applications and data are stored at the mainframe computer, but may be accessed by different users. However, a current trend in network design is to provide a topology that enables distributed processing and peer-to-peer communications. Under this topology, network processing power is distributed among a number of network sites that communicate on a peer-to-peer level. Often, there are a number of servers within the network and each server is accessible by a number of clients. Each server may be dedicated to a particular service, but this is not critical. Servers may communicate with one another in providing a service to a client.
Networks vary significantly in scope. A local area network (LAN) is limited to network connectivity among computers that are in close proximity, typically less than one mile. A metropolitan area network (MAN) provides regional connectivity, such as within a major metropolitan area. A wide area network (WAN) links computers located in different geographical areas, such as the computers of a corporation having business campuses in a number of different cities. A global area network (GAN) provides connectivity among computers in various nations. The most popular GAN is the network commonly referred to as the Internet.
The decentralization of computer networks has increased the complexity of tracking network topology. The network components (i.e., "nodes") may be linked in any one of a variety of schemes. The nodes may include servers, hubs, routers, bridges, and the hardware for linking the various components. Systems for determining and graphically displaying the topology of a computer network are known. U.S. Pat. No. 5,276,789 to Besaw et al. and U.S. Pat. No. 5,185,860 to Wu, both of which are assigned to the assignee of the present invention, describe such systems. As described in Besaw et al., the system retrieves a list of nodes and their interconnections from a database which can be manually built by a network administrator or automatically constructed using computer software. The system can be configured to provide any one of three views. An internet view shows nodes and interconnections of different networks. A network view shows the nodes and interconnections of a single network within the internet view. A segment view displays nodes connected within one segment of one of the networks. Selected nodes on the network, called discovery agents, can convey knowledge of the existence of other nodes. The network discovery system queries these discovery agents and obtains the information necessary to form a graphical display of the topology. The discovery agents can be periodically queried to determine if nodes have been added to the network. In a Transmission Controller Protocol/Internet Protocol (TCP/IP) network, the discovery agents are nodes that respond to queries for an address translation table which translates Internet Protocol (IP) addresses to physical addresses.
The Besaw et al. and Wu systems operate well for graphically displaying hardware components and hardware connections within a network. From this information, a number of conclusions can be drawn regarding the present capabilities and future needs of the network. However, the inter-dependencies of the components in providing a particular service are not apparent from the graphical display that is presented by the system. The complexities of such interdependencies continue to increase in all networks, particularly the Internet. Moreover, these systems are designed in a monolithic manner. This does not allow the management system to be extended to discover and manage new service elements or new services.
Another approach is described by J. L. Hellerstein in an article entitled "A Comparison of Techniques for Diagnosing Performance Problems in Information Systems: Case Study and Analytic Models," IBM Technical Report, September, 1994. Hellerstein proposes a measurement navigation graph (MNG) in which network measurements are represented by nodes and the relationships between the measurements are indicated by directed arcs. The relationships among measurements are used to diagnose problems. However, the approach has limitations, since MNGs only represent relationships among measurements. An ISP operator must understand the details of the measurements (when, where, and how each measurement is performed) and their relationships to the different service elements. This understanding is not readily available using the MNG approach. Furthermore, this publication does not explore ways of automatically discovering the relationships among measurements.
The emergence of a variety of new services, such as World Wide Web (WWW) access, electronic commerce, multimedia conferencing, telecommuting, and virtual private network services, has contributed to the growing interest in network-based services. However, the increasing complexity of the services offered by a particular network causes a reduction in the number of experts having the domain knowledge necessary to diagnose and fix problems rapidly. Within the Internet, Internet Service Providers (ISPs) offer their subscribers a number of complex services. An ISP must handle services that involve multiple complex relationships, not only among their service components (e.g., application servers, hosts, and network links), but also within other services. One example is the web service. This service will be described with reference to FIG. 1. Although it may appear to a subscriber of the ISP 10 that the web service is being exclusively provided by a web application server 12, there are various other services and service elements that contribute to the web service. For instance, to access the web server 12, a Domain Name Service (DNS) server 14 is accessed to provide the subscriber with the IP address of the web site. The access route includes one of the Points of Presence (POP) 16, a hub 18, and a router 20. Each POP houses modem banks, telco connections, and terminal servers. A subscriber request is forwarded to and handled by a web server application. The web page or pages being accessed may be stored on a back-end Network File System (NFS) 22, from which it is delivered to the web server on demand. When the subscriber perceives a degradation in the Quality of Service (QoS), the problem may be due to any of the web service components (e.g., the web application server 12, the host machine on which the web application server is executing, or the network links interconnecting the subscriber to the web server), or may be due to the other infrastructure services on which the web service depends (e.g., DNS or NFS). The ISP system 10 of FIG. 1 is also shown to include an authentication server 24 for performing a subscriber authentication service, a mail server 26 for enabling email service (for login and email access), and front-end and back-end servers 28, 30 and 32 for allowing Usenet access.
Subscribers demand that ISPs offer reliable, predictable services. To meet the expectations of subscribers and to attract new subscribers, ISPs must measure and manage the QoS of their service offerings. This requires a variety of tools that monitor and report on service-level metrics, such as availability and performance of the services, and that provide health reports on the individual service components. Unfortunately, the majority of management systems have not kept pace with the service evolution. Available management systems lack the capability to capture and exploit the inter-relationships that exist among services available in a network environment, such as the Internet. Typically, these management systems discover and manage service elements in isolation. Moreover, these systems are implemented in a monolithic manner and are not easily extensible to discovering and managing new network services and service elements. Adding new discovery and management capabilities to these systems requires extensive redesign and modification of the management system.
Each network is unique in various respects, such as the configuration of servers, the types of application servers, the service offerings, the organizational topology, and the inter-service dependencies. Therefore, in order to accurately understand the operation of the network, specific models must be crafted for the services provided within the network. However, handcrafting models of network services requires an enormous effort on the part of a human expert or group of experts. Furthermore, new Internet services are introduced at a rapid pace. Networking equipment with newer capabilities and faster operation are being introduced rapidly and on an on-going basis. As networks and services evolve, what is needed is a system that is capable of discovering and managing new services and service elements without requiring extensive redesign or modification. Since future services and service elements cannot be predicted with certainty, the system must not be specific to the services and service elements it discovers and manages.
To manage services once they are discovered, what is needed is a method that accommodates the generation of a model of a core service that is available via a network, with the method being responsive to dependencies among services and service elements which are relevant to providing the core service. What is further needed is a system that operates according to the method.